As a portable data terminal such as a mobile phone, a multiband type having two or more communication systems has been developed.
Such a multiband compatible mobile phone sometimes uses a plurality of acoustic wave filters using different pass frequency bands.
Further, an acoustic wave filter which is provided with a function of converting an unbalanced signal and balanced signals has been developed.
The acoustic wave filter provided with the function of converting the unbalanced signal and the balanced signals usually has one input terminal for the unbalanced signal and two output terminals for the balanced signals. Therefore, for example, when it is intended to mount two acoustic wave filters of this type, two input terminals and four output terminals become necessary, so many terminals and lines become necessary.
Therefore, there is known an acoustic wave filter which shares a predetermined terminal among the four output terminals for decreasing the number of terminals and simplifying the lines (see for example Japanese Patent Publication No. 2009-260463A).
However, a conventional acoustic wave filter sharing an output terminal had the problem that the insertion loss easily became worse.
The present invention was devised in order to solve the above problem and has as an object thereof to provide an acoustic wave filter which is resistant to worsening of insertion loss even when an input terminal or output terminal is shared.